JPH0513110Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to a time axis correction device that is applied to remove time axis fluctuations in a video signal reproduced from a recording medium such as a video disk.

[Conventional technology]

Playback color video signals from video discs
FIG. 5 shows an example of a time axis correction device configured to supply the signal to a CCD delay circuit and remove the time axis variation in the reproduced color video signal by controlling the delay time of the CCD delay circuit.

In FIG. 5, a reproduced color video signal, which is optically read from a video disk and formed by FM demodulation, is supplied to an input terminal indicated by 51. This reproduced color video signal is passed through a CCD delay circuit 52, and a stable color video signal (FIG. 6A) from which time axis fluctuations have been removed is taken out at an output terminal 53. The CCD delay circuit 52 includes
Clock pulses are supplied from VCO 54. The oscillation frequency of this VCO 54 is controlled, and the delay time of the CCD delay circuit 52 is varied.

The output color video signal of the CCD delay circuit 52 is
The signal is supplied to a waveform shaping circuit 62 via a bandpass filter 61 having a center frequency of 3.58 MHz, and is also supplied to a synchronous separation circuit 63.

The bandpass filter 61 outputs a color subcarrier component of the chroma signal and a burst signal. In the NTSC system, the phase of the burst signal is inverted every horizontal interval, as shown in FIG. 6A. The waveform shaping circuit 62 is provided to form a pulse waveform having a uniform phase (FIG. 6C) from the output of the bandpass filter 61.

As shown in FIG. 7, the waveform shaping circuit 62 includes limiter amplifiers 71 and 75 and switch circuits 72 and 7.
3. Consists of a bandpass filter 74. The bandpass filter 74 is a high Q filter, such as a ceramic filter, having a center frequency of 3.58 MHz. The output from the bandpass filter 61 is supplied to a limiter amplifier 71 from a terminal indicated by 70 in FIG. limita amp 7
1, the non-inverted output and inverted output of the limiter amplifier 71 are connected to switch circuits 72 and 73.
The signal is supplied to a bandpass filter 74 via the filter.

The switch circuit 72 is supplied with a pulse of frequency (1/2) _H ( _H : horizontal frequency) from a terminal 76. A burst gate pulse is supplied to the switch circuit 73 from a terminal 77 . limita amp 7
The non-inverting output and the inverting output of 1 are connected to the switch circuit 7.
2, the signal is switched every horizontal section, and only the burst signal portion is extracted by the switch circuit 73. Therefore, from the bandpass filter 74,
A burst signal with aligned phases as shown in FIG. 6B is obtained. The output of the bandpass filter 74 is supplied to a limiter amplifier 75 to form a pulse waveform.
The output shown in Figure C is taken from terminal 78.

On the other hand, in FIG. 5, the output of the synchronous separation circuit 63 is supplied to a monomulti (abbreviation for monostable multivibrator) 64. The monomulti 64 is triggered by the leading edge of the horizontal synchronization signal (FIG. 6D) separated by the synchronization separation circuit 63, and the monomulti 64 generates the pulse signal shown in FIG. 6E.
The trailing edge of the output pulse signal of this mono multi 64 triggers the mono multi 65, and the mono multi 6
A gate pulse (FIG. 6F) is generated at the output of 5.

The gate pulse and the shaped burst signal are supplied to an AND gate 66, and only one predetermined wave of the shaped burst signal is taken out at the output of the AND gate 66 as a sampling pulse (FIG. 6G). this
The output signal of the AND gate 66 is the output signal of the CCD delay circuit 5.
This is a phase indicating the time axis fluctuation of the output color video signal of No. 2. The output signal of this AND gate 66 is used as a sampling pulse in the phase comparator circuit 5.
is supplied to one input terminal of 8.

The other input terminal of the phase comparator circuit 58 is supplied with a trapezoidal wave from a trapezoidal wave generating circuit 59 . The trapezoidal wave generating circuit 59 generates the trapezoidal wave shown in FIG. 6I, which is synchronized with a reference horizontal synchronization signal (FIG. 6H) from the terminal 60, which is a time axis reference. The phase comparison circuit 58 is configured as a sampling and holding circuit, and the slope portion of the trapezoidal wave is gated by the sampling pulse. The phase error voltage (J in FIG. 6) generated at the output of the phase comparison circuit 58 is supplied to the control terminal of the VCO 54, and the oscillation frequency of the VCO 54 is controlled.

FIG. 8 shows the time axis correction operation of the above-mentioned time axis correction device. In FIG.
Figure B shows the time variation of the difference between the actual error (dashed waveform 68 in Figure 8A) and the detected error. One step of the error voltage corresponds to one horizontal period.

[Problem that the invention attempts to solve]

The waveform shaping circuit 62 in the above-mentioned conventional time base correction device amplifies the burst signal, inverts each horizontal section, and extracts the burst signal.
limiter amplifiers 71, 75, switch circuit 72,
73 and a bandpass filter 74. For this reason, there was a problem that the number of elements increased and the scale of the circuit increased when integrated circuits were formed. Furthermore, since the processing is performed in separate circuits, there is a problem in that the delay time becomes long.

Therefore, an object of this invention is to provide a time base correction device with a simplified circuit configuration, a reduced number of elements, and a small circuit scale.

Another object of this invention is to provide a time axis correction device with reduced delay time.

[Effect]

Transistors 31 and 32 constitute a differential amplifier. This differential amplifier operates only while a low-level burst signal is supplied to a terminal 48 derived from the bases of transistors 47 whose emitters are commonly connected. A reproduced video signal is supplied to the base of one transistor 31 constituting this differential amplifier via a bandpass filter 11, and burst signals having mutually opposite phases flow through the transistors 31 and 32. Transistor 36,3
7, 38, and 39, burst signals having mutually opposite phases are taken out alternately every horizontal section.

[Means for solving problems]

This invention consists of a burst signal detection circuit to which a reproduced video signal from a recording medium is supplied, a phase comparison circuit for comparing the phase of the burst signal from the burst signal detection circuit with the phase aligned and a reference signal, and The burst signal detection circuit is a time base correction device that includes a time base correction means for removing time base fluctuations of a reproduced video signal using the output of a comparison circuit, and the burst signal detection circuit is based on a phase inversion for each horizontal period. A first transistor 31 to which a reproduced video signal including a burst signal is supplied and a second transistor 32 whose base is connected to a reference power supply have their emitters commonly connected, and a third transistor whose emitters are commonly connected. The connection point of the fourth transistor 36 and 37 is connected to the collector of the first transistor 31, and the connection point of the fifth and sixth transistors 38 and 39, whose emitters are commonly connected, is connected to the collector of the second transistor 32. the bases of the third and sixth transistors 36 and 39 are connected in common, and a reference power source is connected to the connection point; the bases of the fourth and fifth transistors 37 and 38 are commonly connected; In addition, by supplying a signal with a frequency of 1/2 of the horizontal frequency to the connection point and inputting a burst gate pulse to the base thereof, the first and second transistors 31, 31, The emitter of the seventh transistor 47 for disabling the differential amplifier consisting of the transistors 32 and 32 is connected to the emitter connection point of the first and second transistors 31 and 32, and the emitters of the fourth and sixth transistors 37 and 39 are This is a time axis correction device characterized in that it is configured to output phase-aligned burst signals from a collector.

〔Example〕

An embodiment of this invention will be described below with reference to the drawings. FIG. 2 shows an embodiment of this invention.

In FIG. 2, a reproduced color video signal, which is optically read from a video disk and formed by FM demodulation, is supplied to an input terminal indicated by 1. This reproduced color video signal is passed through a CCD delay circuit 2, and a stable color video signal (FIG. 4A) from which time axis fluctuations have been removed is taken out at an output terminal 3. CCD delay circuit 2 is supplied with clock pulses from VCO 4. The oscillation frequency of this VCO 4 is controlled, and the delay time of the CCD delay circuit 2 is varied.

The output color video signal of the CCD delay circuit 2 is supplied to a sampling pulse generation circuit 5, which will be described later. By the sampling pulse generation circuit 5,
A sampling pulse (FIG. 4J) having a phase corresponding to the time axis variation of the output color video signal of the CCD delay circuit 2 is formed. This sampling pulse is supplied to one input terminal of the phase comparison circuit 8.

The other input terminal of the phase comparator circuit 8 is supplied with a trapezoidal wave from a trapezoidal wave generating circuit 9 . The trapezoidal wave generating circuit 9 generates the trapezoidal wave shown in FIG. 4L, which is synchronized with a reference horizontal synchronization signal (FIG. 4K) from the terminal 10, which is a time axis reference. The phase comparison circuit 8 is
It is configured as a sampling and holding circuit, and the slope portion of the trapezoidal wave is gated by the sampling pulse. The phase error voltage (M in FIG. 4) generated at the output of the phase comparison circuit 8 is supplied to the control terminal of the VCO 4, and the oscillation frequency of the VCO 4 is controlled.

The sampling pulse generation circuit 5 has a configuration shown in FIG. In FIG. 3, the output color video signal of the CCD delay circuit 2 is supplied from an input terminal indicated by 6 to a band pass filter 11 having a center frequency of 3.58 MHz and a sync separation circuit 13.

The bandpass filter 11 outputs a color subcarrier component of the chroma signal and a burst signal. In the NTSC system, the phase of the burst signal is inverted every horizontal interval, as shown in FIG. 4A. The output of the bandpass filter 11 is supplied to a waveform shaping circuit 12. Waveform shaping circuit 12
is for forming pulses (FIG. 4C) that are shaped by a burst signal and whose phases are aligned from the output of the bandpass filter 11. The output of the waveform shaping circuit 12 is supplied to one input terminal of the AND gate 16 and is also supplied to the envelope detection circuit 21 .

On the other hand, the output of the synchronous separation circuit 13 is supplied to the monomulti 14.

The monomulti (abbreviation for monostable multivibrator) 14 is triggered by the leading edge of the horizontal synchronization signal (Fig. 4D) separated by the synchronization separation circuit 13, and the pulse signal shown in Fig. 4E is generated from the monomulti 14. do. The trailing edge of the output pulse signal of the monomulti 14 triggers the monomulti 15, and the gate pulse (fourth
Figure F) occurs.

The gate pulse and the shaped burst signal are supplied to the AND gate 16, and only one predetermined wave of the shaped burst signal is extracted at the output of the AND gate 16, as shown in FIG. 4G. This AND gate 16
The output signal of is supplied to the monomulti 23. The monomulti 23 is triggered by the trailing edge of the output signal of the AND gate 16 and generates a narrow reset pulse (FIG. 4H) that falls to a low level. This reset pulse is supplied to the reset terminal of the monomulti 15, and the monomulti 15 is reset at the leading edge of the reset pulse.

A gate pulse (FIG. 4F) generated at the output of the monomulti 15 is supplied to the monomulti 22. Monomulti 22 is triggered on the trailing edge of the gate pulse and generates the sampling pulse shown in FIG. 4J. This sampling pulse is taken out to the output terminal 7. The trailing edge of the gate pulse is defined by the burst signal and has phase information of the color video signal.

Mono multi 15 has capacitor 17 and resistor 18
It has a time constant circuit in which a series circuit of a resistor 19 and a switch 20 is connected in parallel with the resistor 18. This switch 20 is controlled by a detection signal from an envelope detection circuit 21.

The envelope detection circuit 21 is supplied with the shaped burst signal from the waveform shaping circuit 12, and the envelope detection circuit 21 generates a detection signal with a level depending on the presence or absence of the burst signal. As shown in FIG. 4I, the detection signal becomes high level when there is a burst signal, and becomes low level when there is no burst signal. When the detection signal is at a high level, the switch 20 is turned off, and when the detection signal is at a low level, the switch 20 is turned on.

The time constant of the monomulti 15 when the switch 20 is off is determined by the capacitor 17 and the resistor 18. The time constant by this capacitor 17 and resistor 18 includes the position of a predetermined wave of the burst signal (FIG. 4G), as shown by the broken line in FIG. It is set to be slightly longer.

The time constant of the monomulti 15 when the switch 20 is on is determined by the parallel connection of the resistors 18 and 19 and the capacitor 17, and is smaller than the time constant when the switch 20 is off. A resistor is connected so that the pulse width of the output pulse of the monomulti 15 when the switch 20 is on is equal to the pulse width when the monomulti 15 is reset by a predetermined wave of the burst signal when the switch 20 is off. 19 values are selected.

The first half of the waveform diagram shown in FIG. 4 is when a burst signal is present, and the second half of this waveform diagram is when a burst signal is not present, such as during a vertical blanking period. When a burst signal exists, the detection signal of the envelope detection circuit 21 (the fourth
I) becomes high level during the burst signal period. Therefore, the switch 20 is turned off, and a predetermined wave of the burst signal is generated at the output of the AND gate 16, as shown in the first half of FIG.
5 reset pulses (FIG. 4H) are generated.

When there is no burst signal, no pulse signal is generated at the output of the AND gate 16, and the detection signal of the envelope detection circuit 21 becomes low level, as shown in FIG. 4I. Therefore, switch 20
turns on, and the time constant of the monomulti 15 becomes shorter.
Therefore, as shown in FIG. 4F, the monomulti 15
A gate pulse is generated with the same pulse width as when is reset. This gate pulse triggers the monomulti 22, and the monomulti 22 forms the sampling pulse shown in FIG. 4J.

The leading edge of the gate pulse formed by the monomulti 15 is separated from the leading edge of the horizontal synchronization signal by the monomulti 1
It is delayed by a certain period of time specified in 4. Therefore, the leading edge of this gate pulse has phase information of the color video signal indicated by the phase of the horizontal synchronization signal. Therefore, even in a section where no burst signal exists, a sampling pulse (FIG. 4J) having a phase that almost matches the actual time axis variation can be generated, and time axis errors can be continuously detected.

The waveform shaping circuit 12 in the above embodiment is as follows:
It is constructed as shown in FIG.

In FIG. 1, 31 and 32 indicate NPN transistors, and the emitters of the transistors 31 and 32 are commonly connected. This common connection point is grounded via a current source 33, and the transistor 3
1 and 32 constitute a differential amplifier. An input terminal 34 is led out from the base of the transistor 31. A reference power supply 35 is inserted between the base of the transistor 32 and ground.

The emitters of transistors 36 and 37 are commonly connected, and this common connection point is connected to transistor 3.
1 collector. The emitters of transistors 38 and 39 are commonly connected, and this common connection point is connected to the collector of transistor 32. The base of transistor 37 and the base of transistor 38 are connected to each other, and a terminal 40 is led out from this connection point. The base of transistor 36 and the base of transistor 39 are connected to each other, and a reference power source 41 is inserted between this connection point and reference power source 35 .

A collector of transistor 36 and a collector of transistor 38 are connected to power supply terminal 42 . Collector of transistor 37 and transistor 39
The collector is connected to a power supply terminal 42 via a resistor 43 and also to a bandpass filter 44 .

The bandpass filter 44 is a filter having a center frequency of 3.58 MHz, and is made of, for example, a ceramic filter with a high Q. band pass filter 4
The output terminal of 4 is connected to a limiter amplifier 45. An output terminal 46 is led out from the limiter amplifier 45.

Transistors 31 and 3 forming a differential amplifier
A transistor 47 is connected to the common connection point of the two emitters.
The emitters of the two are commonly connected. transistor 47
The collector of is connected to the power supply terminal 42. A terminal 48 is led out from the base of transistor 47.

The color subcarrier component of the chroma signal and the burst signal output from the bandpass filter 11 are supplied to a terminal 34. Frequency (1/2) _H
A pulse of ( _H : horizontal frequency) is supplied to terminal 40, and a burst gate pulse is supplied to terminal 48.

While the burst gate pulse supplied to the terminal 48 is at a low level, the transistors 31 and 32 operate as a differential amplifier. That is, in accordance with the output of the bandpass filter 11 supplied to the terminal 34, a current flows through the transistor 31, and a differential current in the opposite direction flows through the transistor 32. These currents with different directions flow through transistors 36 and 37 and transistors 38 and 3.
9, the frequency (1/2) supplied to terminal 40
It is switched and taken out according to _{the H} pulse.

While the frequency (1/2) _H pulse supplied to the terminal 40 is at a high level, the transistors 37 and 38
is turned on, and transistors 36 and 39 are turned off.
Therefore, an output due to the current flowing through the transistor 31 is supplied to the bandpass filter 44.

While the pulse supplied to the terminal 40 is at a low level, the transistors 36 and 39 are turned on and the transistors 37 and 38 are turned off. Therefore, an output due to the current flowing in the opposite direction through the transistor 32 is supplied to the bandpass filter 44 .

When the burst gate pulse supplied to the terminal 48 becomes high level, the transistors 31 and 32
The potential at the emitter of transistors 31 and 32 is cut off. Therefore, transistors 31 and 32 no longer operate as a differential amplifier.

Therefore, the bandpass filter 44 has terminal 3.
The output of the bandpass filter 11 supplied to the filter 4 is inverted every horizontal section, and the output extracted only during the burst period is supplied. This aligns the phases of the burst signals. A phase-aligned burst signal (FIG. 4B) output from the bandpass filter 44 is supplied to a limiter amplifier 45. The output of the bandpass filter 44 is shaped by a limiter amplifier 45, and a shaped burst signal with aligned phases shown in FIG. 4C is taken out from an output terminal 46.

[Effect of idea]

According to this invention, conventionally, the limiter amplifier 51
and amplification of the burst signal performed by the two switch circuits 52 and 53, inversion for each horizontal section,
A differential amplifier consisting of transistors 31 and 32, a transistor 47, and transistors 36 and 37 operating as a selection circuit extract the burst signal.
, 38 and 39, the circuit scale can be reduced. Transistors 31 and 32
The differential amplifier is configured to operate only during the burst period by connecting the emitters of the transistors 47 to a common emitter connection point. Therefore, the delay time is short.

[Brief explanation of the drawing]

Fig. 1 is a connection diagram of a waveform shaping circuit in an embodiment of this invention, Fig. 2 is a block diagram of an embodiment of this invention, and Fig. 3 is a block diagram of a sampling pulse generation circuit in an embodiment of this invention. , 4th
5 is a block diagram of an example of a conventional time axis correction device. FIG. 6 is a waveform diagram of various parts used to explain a conventional time axis correction device. FIG. 7 is a block diagram of a waveform shaping circuit in a conventional time axis correction device, and FIG. 8 is a schematic diagram for explaining the conventional time axis correction device. Explanation of main symbols in the drawings, 31, 32...
...Transistors forming the differential amplifier, 34...
Input terminal, 40...(1/2) _H pulse input terminal,
47...Transistor for controlling the operation of the differential amplifier, 48...Gate pulse input terminal.

Claims (1)

[Claims for Utility Model Registration] A burst signal detection circuit to which a reproduced video signal from a recording medium is supplied, and a phase comparison between the phase-aligned burst signal from the burst signal detection circuit and a reference signal. A time axis correction device comprising a comparison circuit and a time axis correction means for removing a time axis variation of the reproduced video signal using the output of the phase comparison circuit, the burst signal detection circuit comprising: a base; The first video signal is supplied with the reproduced video signal including a burst signal whose phase is inverted every horizontal period.
The emitters of the transistor 31 and the second transistor 32 whose bases are connected to the reference power source are connected in common, and the connection point of the third and fourth transistors 36 and 37, which have their emitters connected in common, is The fifth and sixth transistors 38 and 39, whose emitters are commonly connected, are connected to the collector of the first transistor 31, and the connection point of the fifth and sixth transistors 38 and 39 is connected to the collector of the second transistor 32; The bases of the transistors 36 and 39 are commonly connected, and a reference power source is connected to the connection point, and the bases of the fourth and fifth transistors 37 and 38 are commonly connected, and the connection point is connected to 1/1 of the horizontal frequency. By supplying a signal with a frequency of 2 and inputting a burst gate pulse to its base, the first and second transistors 31 and 3 operate in a period other than the period including the burst signal.
7 for inactivating the differential amplifier consisting of 2.
The emitter of the transistor 47 is connected to the emitter connection point of the first and second transistors 31 and 32, and a phase-aligned burst signal is output from the collectors of the fourth and sixth transistors 37 and 39. A time axis correction device characterized by: